1. 2018;21;E573-E579Mexiletine Usage in a Chronic Pain Clinic: Indications, Tolerability, and Side Effects
   Retrospective Cohort Study
   Samvid Dwivedi, DO, Joseph Salama-Hanna, MD, and Adam Romman, MD.

BACKGROUND: Intravenous lidocaine has multiple applications in the management of acute and chronic pain. Mexiletine, an oral lidocaine analogue, has been used in a number of chronic pain conditions although its use is not well characterized.

OBJECTIVES: To report our experience using mexiletine in a chronic pain population, specifically looking at tolerability, side effects, and EKG changes.

STUDY DESIGN: Retrospective, cohort study.

SETTING: Three chronic pain clinics within a hospital system in Detroit, MI.

METHODS: All patients who had a mexiletine prescription between August 2015 and August 2016 were queried via the electronic medical record. Each chart was examined for demographics, QTc changes on EKG, length of use, and reasons for stoppage.

RESULTS: There were 74 total patients identified in the chronic pain management clinics as receiving at least 1 mexiletine prescription over the 1-year time period. Twice as many women as men received mexiletine prescriptions. Neuropathic pain was the most common primary diagnosis (64%) which included diabetic neuropathy, radiculopathy, and others. Fibromyalgia was the next most common primary diagnosis (28%). A QTc change on the EKG showed a mean decrease of 0.1 ms and median increase of 1.5 ms. At 6 months (180 days), approximately 30% of the patients remained on mexiletine therapy, and 28% remained on the therapy at 1 year (360 days). Median duration of use was 60 days and the mean was 288 days. Neurologic and gastrointestinal side effects were the most commons reason for stoppage. All side effects were mild and resolved with stoppage. After side effects, lack of response, or loss of efficacy, were the next most common reasons for stoppage.

LIMITATIONS: Pain relief and outcomes were not specifically examined due to confounding factors including interventional treatments and multiple treatment modalities. This was a retrospective, cohort study limited to our specific clinic population with a relatively high loss to follow-up rate.

CONCLUSION: Mexiletine is rarely a first line option for chronic pain management and is often used when multiple other modalities have failed. By reporting our experience, we hope other clinicians may have more familiarity with the drug’s use in a chronic pain practice. It appears reasonably tolerable, may not require frequent EKG monitoring, and can be an appropriate adjunct in the chronic pain population. More research is needed regarding efficacy and dose titration for mexiletine in chronic pain.

KEY WORDS: Chronic pain, mexiletine, IV lidocaine, pain, neuropathic pain, neuropathy, fibromyalgia, QTc, tolerability